Hello everyone, does anybody know a way of incorporating the Herschel-Bulkley (yield Power-Law) rheological model into Fluent? Fluent currently deals with Power-Law non-Newtonian fluids, so can it be modified (maybe by a UDF) to simulate Herschel-Bulkley? If so, how would you go about this? Thanks for any answers in advance!

Hi,

I have implemented yield stress fluids in Fluent : both Bingham and Herschel-Buckley models. It works pretty good. I have programmed an UDF that takes into account the yield stress. In fact, you have to define an UDF for the viscosity using a regularization model to avoid the discontinuity of the model around the yield stress. In my work, I consider the Papanastasiou exponential model for the regularization, but the bi-viscosity model can also be used. Comparisons with analytical solutions in Poiseuille flow in axisymmetric pipes show satisfactory agreement.

Do not hesitate to contact me if you'd like to have some additional informations.

Hope it can help you!!

Anthony

[mehdi27]

Hi Anthony,

I am stuck by modeling Herschel-Bulkley model for a long time. Would you please give me more hints?

I have read your posts and concluded this model based on them;

Apparent viscosity= PV+((1-exp(-m*sr))*yp)/sr
PV: plastic viscosity
yp: yield point
sr: shear rate, in fact the bingham plastic model: shear stress=yp+pv*sr

when I choose m=100, the model works until the end that crashes. However still I get some results which is 2 times the exact solution.
i supposed, if I select very big number for m, for instance 10^6, then I should get better results, but I got very strange numbers.

Would you please help me?

Regards

Originally Posted by Anthony Wachs
;96933

Hi,

I have implemented yield stress fluids in Fluent : both Bingham and Herschel-Buckley models. It works pretty good. I have programmed an UDF that takes into account the yield stress. In fact, you have to define an UDF for the viscosity using a regularization model to avoid the discontinuity of the model around the yield stress. In my work, I consider the Papanastasiou exponential model for the regularization, but the bi-viscosity model can also be used. Comparisons with analytical solutions in Poiseuille flow in axisymmetric pipes show satisfactory agreement.

Do not hesitate to contact me if you'd like to have some additional informations.

Hope it can help you!!

Anthony

[Rahul123]

Hi anthony,
I am also trying to use hershel-bulkley model with papanastasiou approximation. Will only changing the viscosity with a udf do the trick. how will I enter the parameters like n (power index). Where should I attach the udf.

[liliana]

Originally Posted by Anthony Wachs
;96933

Hi,

I have implemented yield stress fluids in Fluent : both Bingham and Herschel-Buckley models. It works pretty good. I have programmed an UDF that takes into account the yield stress. In fact, you have to define an UDF for the viscosity using a regularization model to avoid the discontinuity of the model around the yield stress. In my work, I consider the Papanastasiou exponential model for the regularization, but the bi-viscosity model can also be used. Comparisons with analytical solutions in Poiseuille flow in axisymmetric pipes show satisfactory agreement.

Do not hesitate to contact me if you'd like to have some additional informations.

Hope it can help you!!

Anthony

Hi!

I am trying to simulate a bingham fluid using an UDF in a axysimmetric pipe 2D model and the results are not matching the solutions in poiseuille flow at all...

Would you help me? Can I see your UDF?